The environment-controllable AFM is a precision instrument used to study the surface morphology and physicochemical properties of materials including insulators, based on detecting a weak interaction between a tested sample and the probe, and selecting different working environments such as a vacuum environment, an atmospheric environment, a liquid environment and a varying temperature environment. The environment-controllable AFM, which has played an important role in the fields of surface interface science, materials science and life sciences and promoted the development of nanotechnology, is one of the key instruments for conducting micro-nano scale research. In recent years, with the rapid development of nanotechnology, the demand for environment-controllable AFM is increasing.
Currently, the environment-controllable AFMs can merely carry one probe with a single function. With the gradual deepening of the micro-nano scale research, in many studies, it is necessary to carry out various in-situ detection experiments within the same experimental area on the surface of the sample in a vacuum environment or a same atmospheric environment ((such as nitrogen, oxygen, humidity, alcohol vapor, etc.). For example, in the measurement of friction energy dissipation, other probes with different functions need to be replaced on the premise of not destroying the working environment to realize the in-situ detection. The friction energy dissipation measurement experiment in a vacuum environment is taken as an example. In the vacuum environment, firstly, a probe with a relatively small curvature radius (such as a silicon nitride probe) and a probe of a tip-enhanced Raman spectroscopy were used to perform a surface morphology scanning and a tip-enhanced Raman spectral analysis on an experimental area of a sample surface (the tip-enhanced Raman spectral analysis needs to be carried out with an integrated Raman optical system); secondly, a probe with a relatively large curvature radius (such as a silica pellet probe) was used to conduct microscopic friction and wear on the same experimental area of the sample surface, and a friction curve and other data were recorded; thirdly, the probe with the relatively small curvature radius and the probe of the tip-enhanced Raman spectroscopy were used to perform a surface morphology scanning and a tip-enhanced Raman spectral analysis on the same experimental area of the sample surface after the friction and wear. Based on the comprehensive analysis of all experimental results, the path and rules of friction energy dissipation are inferred, and the mechanism of friction energy dissipation is revealed. However, if the existing environment-controllable AFM is not modified to be equipped with a probe switching device, and the operation process of carrying one probe with a single function for one time is continued, the original working environment will be inevitably destroyed when the chamber is opened for the replacement of other probes with different functions, and many uncertain factors such as oxygen, water vapors and micro-particles in the air will be introduced, resulting in a pollution on the sample surface and a failure of obtaining reliable experimental data. Moreover, the above experimental process is complicated in operation and is inefficient, and after the probe is replaced, it is difficult to find the same experimental area having a nanometer scale to achieve the in-situ detection, which seriously hinders the in-depth study at the micro-nano scale.
However, it is extremely difficult to creatively provide a probe switching device based on an environment-controllable AFM, which is shown as follows:
1. At present, there is no probe switching device suitable for environment-controllable AFM in the scientific research community and industrial community. Only the probe holder and the support for probe holder of the ultra-high vacuum scanning probe microscope have a similar shape to that of the probe switching device. However, from the perspective of essence, the probe holder and the support for probe holder are completely different from the required probe switching device, and the specific details are as follows: (1) The probe holder and the support for probe holder are designed only for the ultra-high vacuum scanning probe microscope, for the functional aspect, the probe holder and the support for probe holder target the ultra-high vacuum environment, rather than the atmospheric environment, liquid environment, etc., required by the environment-controllable AFM. (2) The probe holder and the support for probe holder are very large in size, and unable to be directly transplanted into the environment-controllable AFM with an extremely limited internal space. (3) Since the ultra-high vacuum scanning probe microscope came out, there have been few improvements in the operation of the probe holder and the support for probe holder. The probe is replaced by manually moving the probe holder from the support for probe holder using an external operating lever. The operation is complicated and time-consuming, and it is impossible to quickly switch probes with different functions. (4) The number of positions in the support for probe holder where the probe holder can be placed are limited. The RHK ultra-high vacuum scanning probe microscope is taken as an example, the support for probe holder also serves as a support for sample holder for placing the probe holder and the sample holder at the same time. In order to ensure the smooth operation of the experiment, usually, about half of the positions are used to place the sample holder, and the remaining positions are used to place the probe holder. In addition, the probe holder and the support for probe holder are very expensive. To sum up, from the perspective of essence, the probe holder and the support for probe holder of the ultra-high vacuum scanning probe microscope are completely different from the required probe switching device, and difficult to provide useful reference and guidance.
2. According to the investigation, the design of the existing environment-controllable AFM (mainly the cavity upper cover thereof) focuses on installing one probe with a single function, and no redundant space is left for the modification of the probe switching device (AFM pertains to an ultra-precision instrument. In order to reduce system errors and improve detection accuracy, the mechanical, thermal and optical circuits are required to be designed as short as possible to avoid redundancy). As shown in FIGS. 13-17, the cavity upper cover, the optical window assembly and the probe assembly of the existing environment-controllable AFM are respectively named as original cavity upper cover Y1, original optical window assembly Y2 and original probe assembly Y3 in the present invention. The overall structure of original cavity upper cover Y1 is circular in shape, a circular window is provided in the middle of original cavity upper cover Y1, and original optical window assembly Y2 matched with the circular window is mounted on the upper end surface of original cavity upper cover Y1. Original optical window assembly Y2 is circular in shape, and is composed of circular optical window top cover Y2.3, circular light-transmitting plate Y2.2 and circular optical window hole Y2.1 superposed from top to bottom. Original optical window assembly Y2 is strictly matched with the concave space at the bottom of laser 13 in the diameter and height, without any redundancy. The concave space at the bottom of laser 13 is very limited, having a height of 8 mm, an area of 4239 mm2, and a volume of 33912 mm3. About a half of the concave space is used to install original optical window assembly Y2, while the remaining half of the concave space is used to install original probe assembly Y3 that can carry only one probe with a single function. This remaining half of the concave space can be used for the modification of the probe switching device. However, according to the investigation, currently, the available minimum piezoelectric miniature rotation stage has a volume of 6928 mm3, and coupled with the installation space of the piezoelectric miniature rotation stage, original cavity upper cover Y1 cannot meet the modification requirements of the probe switching device in space. In addition, laser 13 is a key component of the AFM. Once the design of the AFM is finalized, the laser cannot be changed, so it is impossible to carry out the modification from the perspective of expanding the concave space at the bottom of laser 13. To sum up, the existing environment-controllable AFM (mainly the cavity upper cover thereof) has an extremely limited accommodation space, and can only carry one probe with a single function, so the existing environment-controllable AFM cannot be directly modified to be equipped with the probe switching device.
A Chinese patent applied by the present research group is as follows. A multi-probe friction and wear test and in-situ morphology detection system in vacuum (hereinafter referred to as “patent 1”), having an application number of CN 105181501 A, and a publication date of Dec. 23, 2015, includes a main body, and an external manual driving device capable of manually switching probes having different functions in a vacuum environment through a manual method. However, in practical applications, the patent inevitably has the following drawbacks:
1. For this device, the probes with different functions are manually and straightly switched by the external manual driving device. Due to the low precision of the external manual driving device, it is necessary to cooperate with the sample table back and forth when operating the external manual driving device, so as to achieve the positioning of the same experimental area at the nanometer scale. The whole operation is time-consuming, laborious and inefficient.
2. For this device, a very limited number of probes can be carried. According to the design, at most three probes can be carried. In experiments requiring more than three probes (for example, in the friction energy dissipation measurement experiment under the vacuum environment, in order to carry out the friction and wear test between two or more probes and samples, at least four probes are required in total), the device clearly fails to meet the experimental requirements.
In summary, there is an urgent need to creatively provide a probe switching device based on an environment-controllable AFM, which is capable of carrying at least four probes and realizing an efficient and precise switching of probes with different functions through a program control in different working environments such as a vacuum environment, an atmospheric environment, a liquid environment and a varying temperature environment. Therefore, in a same working environment, the functions of the device, i.e., a surface morphology scanning, a Raman spectral analysis, a microscopic friction and wear, and a measurement of friction coefficient, are realized within a same experimental area of a sample surface in situ.